The consumption of isotactic polypropylene approached six billion pounds in 1986. For many years, this important industrial product was produced using catalysts based on titanium trichloride. While such catalysts produced polypropylene with a high degree of isotacticity, their activity was low. To improve the activity of the catalyst, aromatic esters such as ethyl benzoate and ethyl anisate were used in conjunction with the titanium catalyst. Such esters, however, impart an odor to polypropylene and limit its use in such applications as films and fibers.